Angioplasty, an accepted and well known medical practice, involves inserting a catheter containing an uninflated balloon at or near its distal tip into a blood vessel of a patient, and maneuvering the balloon via the catheter through the patient's vessels to the site of a lesion, obstruction, or stenosis. Typically, a physician fluoroscopically guides the catheter fitted with its expandable balloon, from an entry point at the femoral artery, through a patient's arterial system to the site of the stenosis or occlusion. The uninflated balloon portion of the catheter is located within the blood vessel so that it is centered across a lesion, obstruction, stenosis or reduced area. A pressurized inflation fluid is then metered to the uninflated balloon through a lumen in the catheter in order to expand the balloon and thereby dilate the lesion, obstruction, stenosis or restricted area. The inflation fluid is generally a liquid and is applied at relatively high pressure, usually in the area of six to twenty atmospheres. As the balloon is inflated it expands and forces open the previously closed, stenotic or restricted area of the blood vessel. The dilated artery reestablishes an acceptable blood flow through the artery without resorting to more serious, invasive surgical procedures such as grafts or bypasses.
In 1977 the first human coronary balloon angioplasty was performed by Dr. Andreas Gruentzig. This marked the historical beginning of routine clinical use of Percutaneous Transluminal Angioplasty (PCTA). In 1982, one of the earliest patents for an over the wire balloon catheter, U.S. Pat. No. 4,323,071, to Simpson et al., was issued. By 2001 almost two million angioplasties were reportedly performed worldwide, with an estimated increase of 8% annually. The year 2002 marked the 25th anniversary of the first angioplasty performed in an awake patient.
A wide variety of angioplasty balloon and catheter patents are methods are known. References disclosing angioplasty balloons and catheters include:
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The first use of coronary stents in humans was reported in about 1987. By about 1993, the use of a catheter delivered stent to prevent a dilated vessel from reclosing or to reinforce a weakened vessel segment, such as an aneurysm, had become common. A typical procedure for stent installation involves performing an initial balloon angioplasty to open the vessel to a predetermined diameter, removal of the angioplasty balloon catheter, followed by insertion of a delivery catheter carrying the stent and a stent deploying mechanism. The stent is then centered across the opened lesion and then expanded to bring it into contact with the vessel wall by using a balloon as the stent deploying mechanism. The balloon is deflated and the delivery catheter is then removed. The stent deploying balloon is usually larger than the balloon of the predilation catheter. In many cases it has become the practice to then “retouch” the dilation by deploying a third catheter carrying a balloon capable of dilating at a substantially higher pressure to drive the stent into the vessel wall, thereby to assure that there is no risk of the stent later shifting its position and to reduce the occurrence of restenosis or thrombus formation. This “retouch” dilation is often considered necessary when the balloon used to seat the stent is made of a compliant material because such balloons generally cannot be safely pressurized above 9-12 atm., and higher pressures are generally considered necessary to assure full uniform lesion dilation and seating of the stent. In some instances, the same stent-deploying catheter is used to predilate, deploy and seat the stent. Actually this latter situation would be ideal, reducing expense and trauma to the patient.
A wide variety of stent configurations and deployment methods are known. References disclosing stent devices and deployment catheters include:
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Currently drug-eluting stents hold out the promise of dramatically reducing the occurrence of restenosis or the reclosing of balloon dilated arteries. For example refer to U.S. Pat. No. 6,429,232 to Kinsella, et al.
Balloons used in angioplasty procedures are generally fabricated by molding and have predetermined design dimensions such as length, wall thickness and nominal diameter. Balloon catheters come in a large range of sizes and must be suitably dimensioned for their intended use.
Each kind and size of angioplasty balloon has its own expansion characteristics. This expansion characteristic is a factor of both the wall thickness and the material from which the balloon is molded. If the diameter of a balloon is measured during inflation, and the diameter is plotted, as one coordinate, against the inflation pressure as the other coordinate, the resulting curve is called the compliance curve for that particular balloon. It should also be noted that desirable compliance curves are usually linear straight lines. The prior art discloses balloon catheters and methods for making balloon catheters in which the balloons have linear compliance curves. Reference may be had to U.S. Pat. No. 4,490,421 and U.S. Reissue patent U.S. Pat. No. Re. 32,983 and U.S. Pat. No. Re. 33,561 for disclosures of methods for making balloon catheters having linear compliance curves.
If a balloon is made of a material that results in a relatively large increase in diameter when the balloon is inflated to its expanded diameter, such a balloon is said to be a “high-compliant balloon”, “compliant balloon”, “balloon with a high compliance curve”, or “balloon made from compliant plastic material”.
If a balloon is made of a material that results in a relatively small increase in diameter when the balloon is inflated to its expanded diameter, such a balloon is said to be a “non-compliant balloon”, a “balloon made from non compliant plastic material’ or a “balloon with a low compliance curve.
It should be noted that balloons having compliancy curves anywhere between the “high-compliant” and the “non-compliant curves” are available and are generally termed “semi-compliant”.
As typically referred, “non-compliant” balloons are the least elastic angioplasty balloons, increasing in diameter about 2-7%, typically about 5%, as the balloon is pressurized from a inflation pressure of about 6 atm to a pressure of about 12 atm. “Semi-compliant” balloons have somewhat greater elasticity, generally inflating 7-16% and typically 10-12% over the same pressurization range. “Compliant” balloons are still more elastic, inflating generally in the range of 16-40% and typically about 21% over the same pressure range.
All angioplasty balloons have a minimum pressure at which they will burst called the burst pressure. In use a physician is aware of the minimum burst pressure and usually avoids inflating a balloon to the point where it bursts. The burst pressure is determined primarily by the strength of the polymer material from which the balloon is constructed. It should be noted that for a given material, the burst pressure is generally determined by the balloon wall thickness, all other factors being equal.
The strength of polymer materials used in balloon manufacture varies widely. Usually the most inelastic (non-compliant) balloons are also the strongest, being made of highly orientable polymers such as polypropylene, polyethylene terephthalate or other phthalate polyesters or copolyesters, nylons, polyimides, thermoplastic polyimides, polyamides, polyesters, polycarbonates, polyphenylene sulfides, and rigid polyurethanes. “Non-compliant balloons” made from poly(ethylene terephthalate) are commonly referred to as PET balloons. See, U.S. Pat. No. 32,983 to Levy that describes a biaxially oriented, non-compliant polyethylene terephthalate homopolymer (PET) balloon. In addition to PET, other types of materials have been used to produce non-distensible balloons. See, for example, U.S. Pat. Nos. 4,938,676 and 4,906,244 that report using a biaxially oriented nylon or polyamide material, U.S. Pat. Nos. 4,884,573 and 4,952,357 that report using a polyimide material and U.S. Pat. No. 4,950,239 that reports using a polyurethane material. Non-compliant balloons can be characterized as being somewhat in the nature of paper bags that, once inflated to generally remove folding wrinkles, do not further inflate to any significant degree. The higher tensile strengths of nondistensible balloon materials are generally a result of orienting the balloon material during manufacture of the balloon. These materials may have burst pressures that exceed 20 atmospheres (300 psi).
As a general rule, as compliance increases the strength and hence burst pressure of a balloon decreases. Semi-compliant and compliant balloons made of less highly orientable polymers such as thermoplastic elastomers, polyethylene (high density, low density, intermediate density, linear low density), polyesters, polyurethanes, polycarbonates, polyamides, polyvinyl chloride, acrylonitrile-butadiene-styrene copolymers, polyether-polyester copolymers, and polyether-polyamide copolymers, ethylene-vinyl acetate, olefin copolymers, ionomer resins or blends of these materials, have lower strength than those made from the highly orientable polymers such as PET. Their burst pressure might be in the range of 9-10 atm. See, for example, U.S. Pat. No. 4,154,244 to Becker et al. that describes a high compliant thermoplastic rubber balloon. Balloons with a compliance somewhere between “high” and “non-compliant” can be made of nylon or nylon elastomer materials such as Pebax, polyester elastomer materials such as Hytrel or Arnitel or Pelprene, or Thermoplastic polyurethane materials such as Pellethane. Reference to U.S. Pat. No. 5,951,941, by Wang et al, discloses block copolymer elastomer catheter balloons of nylon elastomers and polyester elastomers. See US 2002/0087165 A1 to Lee et al for balloons of thermoplastic polyurethane materials.
While balloons made of non-compliant materials generally possess relatively high tensile strength values, which is a desirable attribute, especially for dilating tough lesions, they may be subject to disadvantageous properties which compromise their utility. For example, PET balloon in particular have been found to be subject to development of pinholes, are fragile and easily damaged during routine handling, and may develop extensive wrinkles when the balloon is sterilized. Furthermore, PET balloon materials do not readily take a fold or a crease. As such when these balloons are collapsed in a deflated state the collapsed balloon flattens and provides an undesired “winged” profile. The phenomenon of “winging” results when the flat, lateral portions of the deflated balloon project laterally outward beyond the rest of the catheter. A “winged” balloon presents a profile having rigid edges that has a much higher likelihood of injuring the arterial system during placement or withdrawal of the balloon. In addition, materials such as PET do not readily accept coating with drugs or lubricants, which can be desirable in many applications. PET is also difficult to fuse, whether by heating or with known biocompatible adhesives. PET and similar non-compliant balloons tend to be stiff, making the dilatation catheter more difficult to maneuver within tortuous vessels. A non-compliant balloon sometimes requires that a physician has to withdraw and replace a balloon that proves to be smaller than needed to fully dilate the artery. Additionally, the use of non-compliant balloons has been considered to be advantageous because they will not inflate significantly beyond their respective designated dilation diameters, thereby minimizing possible damage to vessels due to over-inflation errors. However, assessment of the artery's size can be miscalculated, or arteries may not be uniform and may taper, or may not coincide with readily available catheter balloon dimensions, leaving only the option of withdrawing the non compliant catheter and inserting another more properly sized catheter.
Compliant or semi complaint balloons can provide a wider range of effective inflation or dilation diameters for each particular balloon size because the inflated working profile of the balloon, once achieved, can be further expanded in order to effect additional dilation. Non-Compliant balloons are typically available in size increments of 0.25 mm while High-Compliant balloons typically have size increments of 0.50 mm. This gives the physician some margin of error in matching a specifically sized balloon with the size of the vessel at the stenosis site. An off-sized artery (i.e. 2.90 mm), which is difficult to dilate with a Non-Compliant balloon, can be dilated with a semi compliant or compliant balloon. Thus, fewer models of High-Compliant balloons are required to fill a range of sizes. Another advantage of a High-Compliant balloon over a Non-Compliant balloon is that if a restriction, after being dilated to its desired diameter, recoils when the balloon is deflated, the High-Compliant balloon can be re-inflated to a higher pressure thus dilating the restriction to a diameter greater than its desired diameter resulting in a satisfactory post recoil lumen diameter. This process can be repeated until the restriction retains its desired diameter after deflation of the balloon. High-Compliant balloons also have disadvantages, for example they cannot be successfully used to dilate a hard lesion. Also if a High-Compliant balloon is located across a restriction and an end or both ends of the balloon extend into non restricted areas, when high pressure is applied to the balloon, the pressure may not be sufficient to crack or dilate the restrict area but will dilate the non-restricted area to diameters greater than their normal diameter. In this situation damage can be done to the non-restricted portions of the vessel. Also “high compliant” balloons usually can not reach the high pressures of “non compliant” balloons. The comparatively lower tensile strength of a compliant or semi compliant balloon may increase the risk of possible balloon failure if the balloon is over pressurized. Compliant balloons having high expansion properties also present the risk that a blood vessel may be damaged or ruptured due to uncontrolled overinflation. This is because the expansion at high pressure of many compliant balloons tends to increase in a non-linear manner thereby increasing the risk of uncontrolled overinflation. Manufacturers attempt to cope with lower burst properties and the overinflation risk by increasing balloon wall thickness. Said thicker wall thickness however results in a larger profile and perhaps stiffer catheter thereby reducing its desirability for certain applications.
The particular distension and maximum pressure attributes of a balloon are influenced not only by polymer type but also by the conditions under which the balloon is blown. Angioplasty balloons are conventionally made by blow molding a tube of polymer material at a temperature above its glass transition temperature. For any given balloon material, there will be a range of distensions achievable depending on the conditions chosen for the blowing of the balloon. For example by controlling blowing conditions such as initial dimensions of tubing, pre-stretch, hoop ratio and heat set conditions, one can vary the compliance characteristics and wall strength of a balloon to some degree. In U.S. Pat. No. 6,110,142 to Pinchuck there are described balloons of nylon that exhibit variable characteristics depending on how they are blown. The data in the reference show that compliance characteristics can be obtained ranging from non-compliant to semi-compliant characteristics and that wall strengths of greater than 15,000 psi can be obtained. According to the author, the balloons exhibit the ability to be “tailored” to have expansion properties that are desired for a particular end use. However, the degree of “tailorability” is limited according to the disclosures to an expansion of at most 35 or 40%.
Due to the limitations inherent in current balloon technology discussed above, it would be desirable to have a balloon catheter which exhibits the wide expansion characteristics of a compliant balloon, but is capable of operating at a high pressure similar to a non compliant balloon, but without the danger of overinflation.
Compliance curves of angioplasty balloons, in their usable range are linear, that is essentially a straight line. As a result a physicians choice, in the past, has been to select a balloon having a linear compliance curve that best meets his needs. Sometimes, Physicians encounter medical situations where an angioplasty balloon having a nonlinear compliance curve is desired. For example a physician may have a medical situation in which he desires a balloon that will during the initial inflation phase increase in diameter by 20% and then in the secondary inflation phase become very rigid and hard with little further increase in diameter. Another example might be the situation where two lesions are encountered, one that can be treated with a High-Compliant balloon and the other that requires a Non-Compliant balloon. Using two balloon catheters in such a situation, which the initial High-Compliant balloon must be removed and replaced with a Non-Compliant balloon, has the disadvantage exposing the patient to the trauma of removing and replacing a balloon catheter, a longer procedure time, and the expense of two balloon catheters. These disadvantages can be avoided by use of a balloon catheter that has a nonlinear or hybrid compliance curve.
In U.S. Pat. Nos. 5,348,538; 5,403,340; and 5,500,181 to Wang et al, there is described a single layer balloon which follows a stepped compliance curve. The stepped compliance curves of said balloon has a lower pressure segment following a first generally linear profile, a transition region, typically in the 8-14 atm range, during which the balloon rapidly expands yielding inelastically, and a higher pressure region in which the balloon expands along a generally linear, low compliance curve. It is claimed that the stepped compliance curve allows a physician to dilate different sized lesions without using multiple balloon catheters. In U.S. Pat. No. 5,490,838 to Miller, there is disclosed a balloon catheter which can be expanded in a stepped fashion to two different known, work hardened diameters. In U.S. Pat. Nos. 6,290,485; and 6,402,778; there is disclosed a method for installing a stent using a single balloon catheter with a stepped compliance curve. Claimed is a single stent deploying catheter for both low pressure predilation and subsequent high pressure embedding of the stent in the vessel wall. However the devices disclosed involve dilation catheters with relatively thick walled balloons, thereby limiting their utility in many applications. For example, in Wang, the stepped compliance curve is obtained by an unusual annealing technique. The entire balloon catheter is submerged in water or air at a temperature in the range of 25-100 degree Centigrade for 3-180 minutes, the temperature and time required in this annealing process, depending upon the size of the balloon that is being processed. This annealing process causes the length and the diameter of the balloon to decrease and the wall thickness to increase which results in a balloon catheter with a hybrid compliance curve. The relatively thick wall balloon of Wang results from allowing the balloon to shrink both axially and radially.
It would be desirable to have or be able to manufacture a series of improved medical dilation catheters for angioplasty, stent deployment or other usages containing a dilation element with linear or non linear expansion characteristics, and/or with higher compliance characteristics and/or with reduced risk of overinflation at high pressure and/or a balloon element of whose profile is the same as the tube from which it was formed.
Thus fabricating an angioplasty balloon places conflicting demands on the materials used to obtain extremely thin walled high strength relatively inelastic balloons of predictable and desirable inflation properties. These conflicting demands usually result in a trade off of properties with certain characteristics being balanced against others. For example, a minimum balloon profile is advantageous because it allows the balloon to easily reach and then traverse tight stenosis or occlusions with minimum trauma to arterial vessels. This requires a thin walled balloon that tends to lower the burst pressure of the balloon. In order to maintain the higher burst pressure of a balloon in order to push open a stenosis easily, a very high strength material must be used so the thin wall will not burst under the high internal pressures necessary to accomplish this task. But high strength materials tend to be fragile, stiff and very inelastic. However, it its desirable that the balloon be flexible and have some elasticity so that the inflated diameter can be controlled, and to allow the surgeon to vary the balloon's diameter as required to treat individual lesions, yet still be able to compensate for variations in vessel walls or “recoil” as well as be maneuverable through tortuous vessels. However, elasticity must be relatively low to avoid overinflation and damage to the vessel. In addition the diameter must easily controllable with pressure so that small variations in pressure will not cause wide variation in diameter.
Medical balloons typically retain their shape when in the unpressurized state somewhat like a collapsed paper bag. In order to maintain a low crossing profile, the collapsed balloon must be wrapped tightly around itself. The current art allows a minimum balloon profile by minimizing the wall thickness of the balloon material. This allows for a low profile by enabling a collapsed balloon to be wrapped around itself multiple times without appreciably increasing the diameter of the area contained the collapsed wrapped balloon. But the thinner wall gives a weaker balloon and thus reduces the amount of pressure that can safely be used to inflate the balloon and open a stenosis. This requires the use of very strong materials to allow for the required minimum balloon wall thickness and usually yields a rigid, hard, stiff balloon. Use of a more elastomeric material that tend to be flexible, soft and deformable yields either a weaker balloon, which may overinflate and damage the vessel or burst at too low a pressure, or a thicker balloon which presents an unacceptable profile.
The design of a balloon therefore is a compromise and it was thought unlikely to obtain a high compliant, high-pressure balloon, flexible, low profile balloon with a linear or non-linear compliance curve within a single balloon. Therefore, there is still a need for improved materials and method for inflatable medical balloon elements.